We tested the 400x lens in 2005 and we decided not to carry it. Because of the high magnification, this lens has a very narrow depth-of-field, which makes it very difficult to use as a handheld unit. In our tests, anything above 200x magnification worked much better with a ProScope attached to a traditional microscope. This allows for much, much higher magnification, and the fact that it is mounted takes out any unsteadiness. We can special order it if you like (ProScope 400X Lens, order code BD-400x, $259), but we always give a word of caution before doing so.
We also carry a Celestron Digital Microscope Imager which fits into the ocular tube of a microscope and offers a 1 MP image of the specimen being viewed. (Celestron Digital Microscope Imager (2 Megapixel), order code CS-DMI, $79)